Recovery of tocopherol and sterol from tocopherol and sterol containing mixtures of fats and fat derivatives

ABSTRACT

A process is provided for simultaneously recovering tocopherol and sterol from a mixture containing tocopherol, fats and/or fat derivatives, more particularly fatty acids, and sterol and/or sterol derivatives, more particularly from a steamer distillate of natural oils and fats. The steps of said process comprise: 
     free fatty acids present in the mixture are esterified with a lower alcohol, preferably methanol, 0.4 to 1.6 and more particularly 1 to 1.5 parts by volume of mixture being esterified with 1 part by volume of the lower alcohol, 
     the mixture is subsequently transesterified with the lower alcohol in the presence of a basic catalyst, 
     the excess lower alcohol is distilled off from the reaction mixture after the transesterification, 
     the transesterification catalyst and the glycerol optionally present are removed, more particularly by washing, 
     the fatty acid alkyl ester is distilled off from the mixture, more particularly after removal of the transesterification catalyst, and 
     if desired, tocopherol and sterol are separated by methods known per se. After the transesterification reaction, the alkali catalyst is preferably neutralized with an inorganic acid and the mixture is then washed with water.

This application is a 371 of PCT/EP93/02207 filed Aug. 18, 1993.

This application is a 371 of PCT/EP93/02207 filed Aug. 18, 1993.

BACKGROUND OF THE INVENTION AND FIELD OF THE INVENTION

This invention relates to a process for simultaneously recoveringtocopherol and sterol from a mixture containing tocopherol, fats and/orfat derivatives, more particularly fatty acids, and sterol and/or sterolderivatives, more particularly from a steamer distillate of natural oilsand fats.

A DISCUSSION OF RELATED ART

Tocopherol compounds occur in many vegetable and animal oils and arealso referred to as vitamin E. The vitamin E relates to thephysiological effect of these food ingredients.

There are 8 naturally occurring substances with vitamin E activity. Theyare derivatives of 6-chromanol and belong to two groups of compounds.The first group is derived from tocol and carries a saturatedisopren-oidal side chain containing 16 carbon atoms. This group includesalpha-, beta-, gamma- and delta-tocopherol. The compounds differ intheir degree of methylation at the benzene ring of the tocol.Alpha-tocopherol is the substance with the strongest biological vitaminE activity and the greatest technical and economical importance. It isthe dominant tocopherol in human and animal tissue.

The second group of substances with vitamin E activity are thederivatives of tocotrienol. They differ from the other tocopherolhomologs in the unsaturated isoprenoidal side chain containing 16 carbonatoms. The naturally occurring tocoenols also show vitamin E activityand are normally isolated from their natural sources together with thesaturated tocopherol homologs in the recovery of vitamin E. In thecontext of the present invention, the name "tocopherol" is also intendedto encompass these tocopherol homologs, i.e. any substances with vitaminE activity.

By virtue of their oxidation-inhibiting properties, the tocopherols areused in foods and in cosmetics and pharmaceuticals and as an additive inpaints based on natural oils.

In the context of the invention, the name "sterol" encompasses thesterols which are also known as stearins. The names "sterol" and"stearin" are used synonymously in the present context. The sterols aremonohydric secondary steriod alcohols containing 27 to 30 carbon atomswhich have the basic structure of gonane. The carbon atom 3 of gonanebears the hydroxyl group. The structural differences between theindividual sterols hitherto occurring in nature lie in the presence ofdouble bonds in the ring system, in the appearance of substituents inpreferred positions and in the constitution of the side chain which isanchored to carbon atom 17 of gonane.

The most important representative of the sterols is cholesterol whichoccurs in free or esterified form in animal organs and liquids,particularly in the brain, in the spinal cord, in the suprenal glands,in liver oil and in wool grease. Cholesterol belongs the so-calledzoosterols which is the name given to the sterols present in animalfats. Vegetable sterols are called phytosterols. The most importantrepresentatives are ergosterol, stigmasterol, campesterol andsitosterol. The stearins or sterols are valuable starting materials inthe synthesis of pharmaceuticals, particularly steroid hormones, forexample corticosteroids and gestogens. For example, stigmasterol canreadily be converted into progesterone.

The starting mixtures for the recovery of tocopherol and sterol may beany of a number of vegetable and animal substances. The highestconcentrations of tocopherol are found in vegetable oils, such aswheatgerm oil, corn oil, soybean oil and palm kernel oil. However,tocopherol is also found in other vegetable oils, for example insafflower oil, peanut oil, cottonseed oil, sunflower oil, rapeseed oil,palm oil and other vegetable oils.

The natural plant oils contain only small quantities of tocopherol.Concentration is undesirable for commercial applications. In addition,impurities are supposed to be removed to enhance the antioxidizingeffect and vitamin E activity. Accordingly, the most important naturalsources of tocopherol are not the vegetable oils themselves, but ratherthe steam distillates--also known as steamer distillates--obtained inthe deodorization of vegetable and animal oils. Although the tocopherolsare obtained in concentrated form, they are mixed with sterol and sterolesters, free fatty acids and triglycerides. The distillate from thedeodorization of soybean oil is particularly interesting. The particularsuitability of soybean oil as a source of tocopherols is mentioned, forexample, in Fat Sci. Technol., Vol. 91, 1989, pages 39 to 41 in acomparison of the deodorization distillates of soybean oil and rapeseedoil. The soybean oil steamer distillate contains approximately 10 Ma %mixed tocopherols and the same amount of sterols which are predominantlypresent in their ester form.

There are various known processes for the concentration of tocopherol,namely esterification, saponification and fractional extraction. Thus,according to DE 31 26 110 A1, tocopherol concentrates are obtained fromsecondary products of the deodorization of oils and fats byesterification of the free fatty acids present therein by addition of analcohol or by removal of the free fatty acids from the distillates bydistillation, after which these products are subjected to hydrogenationand subsequently to solvent fractionation to extract the tocopherols.Another process for concentrating tocopherol is known from the samedocument. In this process, the deodorization distillates are subjectedto transesterification with methanol and the fatty acid methyl estersare distilled off. The residue is concentrated by moleculardistillation.

In another process known from EP 171 009 A2, the tocopherol-containingmaterial is contacted with a sufficient quantity of a polar organicsolvent which dissolves the tocopherols, but not the impurities. Thepolar phase enriched with tocopherol is separated off and the tocopherolis recovered therefrom.

It is also known that the tocopherols can be separated by adsorptiononto basic anion exchangers. This variant is possible if the mixturecontains little, if any, fatty acid. The sterols, glycerides and otherneutral or basic substances are not adsorbed (Ullmanns Enzyklop adie dertechnischen Chemie, 4th Edition, Vol. 23, 1984, page 645).

In one Example, GB 2 145 079 A describes the use of acidic ionexchangers as a catalyst for the esterification of free fatty acidspresent in rapeseed oil distillate with 5 parts by volume of methanol to1 part by volume of deodorization distillate. Because constituentsinsoluble in methanol accumulate, the esterification is carried out in afluidized bed. The need for the fluidized bed complicates the processand makes it uneconomical to carry out on an industrial scale.

In another process known from EP 333 472 A2 for the production of highlyconcentrated products containing tocopherol and tocotrienol from palmoil steamer distillate, it is only possible to recover tocopherol andnot sterol. This is because reaction times of around 2 hours arerequired for the transesterification of sterol esters in view of therelatively low reaction rates and are not achieved with the reactiontimes of 10 minutes sufficient in this process and for thetransesterification of glycerides.

It is also known that sterols can be separated from tocopherols byfractional crystallization after concentration. In this process,tocopherol passes into solution and sterol crystallizes out. Tocopheroland sterol can also be separated by distillation, except that in thiscase the sterol is at least partly destroyed.

Known processes for the recovery of tocopherol and sterol are attendedby various disadvantages.

The extraction processes often have to be adapted to the startingmixture because the impurities present therein have a considerablebearing on extraction and the desired useful products, tocopherol andsterol, do not always pass into the desired phase with the sameextraction process and different starting mixtures. In addition, knownextraction processes use physiologically unsafe solvents.

Ion exchangers have a specific effect on the starting material, requirethorough preliminary purification of the mixture and do not allowtocopherol and sterol to be simultaneously concentrated.

In a variant described in DE 31 26 110 A1, tocopherol is subjected tomolecular distillation or to steam distillation after esterification ofthe free fatty acids with polyhydric alcohols in order to obtain adistillate having a high tocopherol content. However, the process stepof molecular distillation is uneconomical on an industrial scale whilesteam distillation involves exposure to relatively high temperatureswhich at least partly destroys the sterols. In the latter case,therefore, only the thermally more stable tocopherol can be obtained inhigh yields.

A DESCRIPTION OF THE INVENTION

Accordingly, the problem addressed by the present invention was toprovide a process for the simultaneous recovery of tocopherol and sterolwhich would be applicable to many different starting mixtures and whichwould not use any toxicologically or ecologically unsafe solvents, wouldnot involve exposure to high temperatures, would give high yields andwould be economically workable on an industrial scale.

According to the invention, the solution to this problem ischaracterized in that

1) free fatty acids present in the mixture are esterified with a loweralcohol, preferably methanol, 0.4 to 1.6 and more particularly 1 to 1.5parts by volume of mixture being esterified with 1 part by volume of thelower alcohol,

2) the mixture is subsequently transesterified with the lower alcohol inthe presence of a basic catalyst,

3) the excess lower alcohol is distilled off from the reaction mixtureafter the transesterification,

4) the transesterification catalyst and optionally the glycerol presentare removed, more particularly by washing,

5) the fatty acid alkyl ester is distilled off from the mixture, moreparticularly after removal of the transesterification catalyst, and

6) if desired, tocopherol and sterol are separated by methods known perse.

In a first step, the free fatty acids present in the starting mixtureare reacted with a lower alcohol to form fatty acid alkyl ester, moreparticularly fatty acid methyl ester, in order to rule out asaponification reaction with the transesterification catalyst used inthe next step. Particularly high reaction rates can be achieved with theabove-mentioned range of 1 to 1.5 parts by volume of mixture to loweralcohol. In the case of mixtures with no free fatty acids, this firststep may be omitted. In the following process step, transesterificationthe sterol fatty acid ester is reacted to sterol and fatty acid methylester. The partial glycerides and triglycerides react to form glyceroland fatty acid methyl ester. The tocopherol present in the mixture doesnot react. In many cases, not only tocopherols, but also tocopherolesters are present in the starting mixture, for example in the soybeanoil steamer distillate with 0.5 Ma %. In this step, the esters areconverted into tocopherols. For the next process step, removal of theexcess lower alcohol by distillation, it is of particular advantage if ashort-chain alcohol, more particularly methanol, has been used in thepreceding steps. In this way, exposure to high temperatures can beminimized. Before removal of the fatty acid alkyl ester by distillation,it is advisable not only to separate the glycerol formed in thetransesterification step from triglycerides present, if any, but also toremove the transesterification catalyst. The catalyst is largely presentin the form of alkali metal soap which could be problematical duringdistillation and could lead, for example, to an increase in the boilingpoint. A highly concentrated tocopherol/sterol mixture is obtained afterremoval of the fatty acid alkyl ester. The tocopherol and sterol in thismixture can be separated from one another by methods known per se, forexample by crystallization.

A major advantage of the process according to the invention is that itcan be applied to various mixtures containing tocopherol and,optionally, sterol. In particular, however, it is of advantage to startout from soybean oil steamer distillate which is obtained by steamdistillation of crude soybean oil as the first stage of thedeodorization process. The distillate contains approximately 20% ofsterol, 8% of tocopherol, 20% of free fatty acids and, as its principalconstituent, triglycerides (Ullmann, loc. cit.).

However, steamer distillates of other oils, for example rapeseed oildistillates, can also be processed by the process according to theinvention.

The process according to the invention is by no means limited in itsapplication to steamer distillates of vegetable oils and fats. It mayalso be applied with advantage to tall oil. Tall oil is, economically,one of the most important secondary products of the cellulose sulfateprocess used in papermaking. It is obtained by acidification of thesodium salt mixture of resinic and fatty acids formed in this process.Tall oil is a natural mixture of resinic acids of the abietic acid type,saturated and unsaturated fatty acids and fatty acid esters and anunsaponifiable fraction. In addition to higher alcohols andhydrocarbons, the unsaponifiable fraction also contains sterols.

Other mixtures containing tocopherol may also be worked up by theprocess according to the invention, for example the residue obtained inthe production of rapeseed oil methyl ester which also contains sterolsand sterol esters.

In one preferred embodiment of the process according to the invention,the fatty acids are esterified in the presence of a strongly acidic ionexchanger, more particularly present in a fixed-bed reactor, attemperatures in the range from 60° to 100° C. and more particularly attemperatures in the range from 65° to 70° C. The distinctly smaller lossof tocopherol through its solubility in methanol than occurs in theremoval of the fatty acids by distillation was both advantageous andsurprising. In the esterification of the fatty acids, the ratio of thevolume streams between steamer distillate and lower alcohol is between1.1 and 1.7 and preferably 1.4. The residence time in the fixed-bedreactor is 1 to 2 hours and preferably 1.6 hours. These figures apply tothe free volume actually present. In esterification, the fatty acidspresent in the mixture are reacted to fatty acid alkyl ester at theactive centers of the strongly acidic ion exchanger.

After the reaction, the excess lower alcohol, i.e. generally methanol,is removed in a phase separator. The alcohol additionally contains thepredominant part of the water formed during the esterification.

After the transesterification and the removal of the excess alcohol fromthe reaction mixture, the catalyst and any glycerol present are removedfrom the mixture. The catalyst is preferably neutralized beforehand byacidification with an inorganic acid.

The following Examples are intended to illustrate the invention withoutlimiting it in any way.

EXAMPLES Example 1

Esterification of the Fatty Acids

Soya steamer distillate having an acid value of 70 was introduced at avolumetric flow rate of 0.094 l/h together with 0.067 l/h methanol intoa 0.3 m long glass column charged with catalyst, namely a stronglyacidic macroporous ion exchanger resin (Lewatit K 2631). The diameter ofthe column was 0.07 m. After a residence time of 1.6 h, the mixture wascollected in a glass vessel and decanted. Subsequent concentration byevaporation to separate the methanol/water mixture from the fatty phasewas carried out in vacuo. The acid value was subsequently determined at1.3, corresponding to a conversion of 98%, i.e. the loss of tocopherolwas negligible. Accordingly, the material has been deacidified for thefollowing transesterification step.

Example 2

Transesterification of the Glycerides and Sterol Esters

The soya steamer distillate deacidified in the first step (acid valueapprox. 1) was contacted with methanol and the basic catalyst in a tubereactor. The reaction temperature was between 60° and 90° C. andpreferably 65° C. Based on the soya steamer distillate used, 40 to 80%of methanol (preferably 50 to 60%) and 0.8 to 1.5% of catalyst(preferably 1%) were used. Sodium methylate was preferably used as thecatalyst, although other basic catalysts, for example sodium, potassiumand lithium hydroxide, etc., may also be used. The reaction time wasapprox. 2 h at 65° C. After the transesterification, at least 90% of thesterol esters and at least 95% of the glycerides had been reacted.

Example 3

Transesterification of the Glycerides and Sterol Esters

2.8 kg of deacidified soya steamer distillate, acid value 1.9, werecontacted with 1.4 kg of methanol in which 192 g of 30% methanolicsodium methylate had been dissolved. The mixture was heated withcontinuous stirring to 65° C. and was kept at that temperature for 2 h.To avoid losses of tocopherol, a nitrogen atmosphere was established.

The starting mixture contained approximately 6% of free sterols, a valueof 16% being determined after transesterification following removal ofthe methanol component. The initial glyceride content of 25% fell to1.2%. 90% of the glycerides were monoglycerides. Triglycerides could nolonger be detected.

Example 4

Removal of the Excess Methanol and Separation of Catalyst And Glycerol

After the transesterification, the excess methanol was distilled offfrom the reaction mixture at a temperature of 90° C./100 mbar.

The demethanolized reaction mixture contained the catalyst used mainlyin the form of the alkali metal soap. To remove the catalyst from thesteamer distillate, 2.2 kg of demethanolized soya steamer distillatewere acidified with 148 g of 3% hydrochloric acid and washed with 1.1 kgof water. Both phases were separated in a decanter.

Example 5

Separation of the Methyl Ester

After distillation of the methyl ester formed from the product ofExample 4, a mixture containing 40 Ma % of free sterols and 30 Ma % oftocopherols was obtained.

We claim:
 1. A process for the recovery of tocopherol and sterolconcentrates from tocopherol- and sterol-containing mixtures of fats andfat derivatives comprising:(a) esterifying free fatty acids in saidmixture with methanol in the presence of a solid acidic catalyst, toform an esterified mixture containing fatty acid methyl esters; (b)separating the solid acidic catalyst from the esterified mixture; (c)removing water from the esterified mixture to form a dried esterifiedmixture; (d) transesterifying triglycerides in said dried esterifiedmixture by alkali-catalyzed transesterification with methanol to form atransesterified mixture; (e) removing unreacted methanol from thetransesterified mixture to form a demethanolized mixture; (f) removingakali catalyst from the demethanolized mixture by acidifying and thenwashing the demethanolized mixture to form a washed mixture; and (g)removing by distillation fatty acid methyl esters from the washedmixture.
 2. The process as claimed in claim 1 wherein steamerdistillates of soybean oil are used as the mixtures of fats and/or fatderivatives.
 3. The process as claimed in claim 1 wherein saidacidifying is effective to neutralize the alkali of saidalkali-catalyzed transesterification.
 4. The process as claimed in claim1 wherein an inorganic acid is used in said acidifying.
 5. The processas claimed in claim 4 wherein said inorganic acid is hydrochloric acid.6. The process of claim 1 wherein water is used in said washing.
 7. Theprocess of claim 1 wherein in said esterifying of said free fatty acids,0.4 to 1.6parts by volume of mixture is esterified using 1 part byvolume of methanol.
 8. The process of claim 7 wherein 1 to 1.5 parts byvolume of mixture is esterified using 1 part by volume of methanol. 9.The process as claimed in claim 2 wherein said free fatty acids areesterified at temperatures of 60° to 100° C. in the presence of astrongly acidic ion exchanger.
 10. The process as claimed in claim 9wherein said esterifying is carried out in a fixed-bed reactor.
 11. Theprocess as claimed in claim 9 wherein said temperatures are 65° to 70°C.
 12. A process for the recovery of tocopherol and sterol concentratesfrom tocopherol and sterol-containing mixtures of fats and fatderivatives comprising:(a) esterifying free fatty acids in said mixturewith methanol, said mixture being a steamer distillate of soybean oil,in the presence of a solid acidic catalyst to form an esterified mixturecontaining fatty acid methyl esters; (b) separating the acidic catalystfrom the esterified mixtures; (c) removing water from the esterifiedmixture to form a dried esterified mixture; (d) transesterifyingtriglycerides in said dried esterified mixture by alkali-catalyzedtransesterification with methnol to form a transesterified mixture; (e)removing unreacted methanol from the transesterified mixture to form ademethanolized mixture; (f) acidifying the demethanolized mixture toneutralize said demethanolized mixture and then washing thedemethanolized mixture with water to form a washed mixture; and (g)removing by distillation fatty acid methyl esters from the washedmixture to recover a mixture comprising tocopherol and sterol.